Sp6 and Sp8 transcription factors control AER formation and dorsal-ventral patterning in limb development

PLoS Genet. 2014 Aug 28;10(8):e1004468. doi: 10.1371/journal.pgen.1004468. eCollection 2014 Aug.

Abstract

The formation and maintenance of the apical ectodermal ridge (AER) is critical for the outgrowth and patterning of the vertebrate limb. The induction of the AER is a complex process that relies on integrated interactions among the Fgf, Wnt, and Bmp signaling pathways that operate within the ectoderm and between the ectoderm and the mesoderm of the early limb bud. The transcription factors Sp6 and Sp8 are expressed in the limb ectoderm and AER during limb development. Sp6 mutant mice display a mild syndactyly phenotype while Sp8 mutants exhibit severe limb truncations. Both mutants show defects in AER maturation and in dorsal-ventral patterning. To gain further insights into the role Sp6 and Sp8 play in limb development, we have produced mice lacking both Sp6 and Sp8 activity in the limb ectoderm. Remarkably, the elimination or significant reduction in Sp6;Sp8 gene dosage leads to tetra-amelia; initial budding occurs, but neither Fgf8 nor En1 are activated. Mutants bearing a single functional allele of Sp8 (Sp6-/-;Sp8+/-) exhibit a split-hand/foot malformation phenotype with double dorsal digit tips probably due to an irregular and immature AER that is not maintained in the center of the bud and on the abnormal expansion of Wnt7a expression to the ventral ectoderm. Our data are compatible with Sp6 and Sp8 working together and in a dose-dependent manner as indispensable mediators of Wnt/βcatenin and Bmp signaling in the limb ectoderm. We suggest that the function of these factors links proximal-distal and dorsal-ventral patterning.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Body Patterning / genetics*
  • DNA-Binding Proteins / biosynthesis*
  • DNA-Binding Proteins / genetics
  • Ectoderm
  • Embryo, Mammalian
  • Embryonic Development
  • Extremities / embryology
  • Extremities / growth & development*
  • Gene Dosage
  • Gene Expression Regulation, Developmental
  • Kruppel-Like Transcription Factors / biosynthesis*
  • Kruppel-Like Transcription Factors / genetics
  • Mice
  • Signal Transduction / genetics
  • Transcription Factors / biosynthesis*
  • Transcription Factors / genetics
  • Wnt Proteins / biosynthesis
  • Wnt Proteins / genetics

Substances

  • DNA-Binding Proteins
  • Kruppel-Like Transcription Factors
  • Sp6 protein, mouse
  • Sp8 protein, mouse
  • Transcription Factors
  • Wnt Proteins
  • Wnt7a protein, mouse

Grant support

Supported by grant BFU2011-24972 from the Spanish Government (MAR) and by National Organization of Rare Diseases (KCO) and by the Intramural Research Program at the National Institute of Dental and Craniofacial Research, NIH, USA (YY). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.